none of your concern

What people say when you get too nosy.

Also what people say when you ask for too many details.

Hey Sam, I slept with this guy a few months ago
What? When? Who?

Nevermind. It is none of your concern.

None of your concern

Another way of saying “none of your business”

Teacher: I gotta go on a date tomorrow so you’ll have a substitute

Student: Ooh, who are you going on a date with?
Teacher: That’s none of your concern